The present invention relates to a semiconductor device and a method of fabricating the same and, particularly, to an aluminum wiring to be used as electrode wiring of a semiconductor integrated circuit and a method of forming the same wiring.
It has been usual that a wiring of aluminum film is used as an electrode wiring of a semiconductor integrated circuit, in particular, a silicon large scale integrated circuit (Si-LSI), for reasons of high compatibility with aluminum to a silicon substrate, easiness of machining and good adhesion to a lower layer, etc.
With increase of integration density of semiconductor integrated circuit, density of current flowing through an electrode wiring increases, causing reliability problem of aluminum film wiring to come to surface. The problem may include reliability of contact to shallow junction, inter-wiring short-circuit due to hillocks and wiring breakage due to stress migration and/or electromigration.
The problem of contact reliability can be excluded by use of wiring of aluminum and silicon (Al-Si) alloy film and an insertion of a barrier film of such as titanium nitride (TiN) between an impurity diffusion layer and an aluminum film wiring for the purpose of preventing silicon diffusion from the diffusion layer to the aluminum film. However, when such titanium nitride film is covered by the aluminum film, grain size of aluminum of the latter may be reduced, degrading resistance thereof to electromigration.
Generation of hillock can be reduced by using, as wiring, a multi layer film composed of an alternative lamination of aluminum-silicon alloy films and titanium films, as disclosed in U.S. Pat. No. 4,673,623 issued on Jun. 16, 1987 to D. S. Gardner et al. and assigned to The Board of Trustees of the Leland Stanford Junior University. However, in Gardner et al., thickness of the titanium film contributes largely to properties of a resultant wiring such that, when thickness is reduced, possibility of hillock generation is increased, while, when it is increased, resistance thereof is increased. Therefore, in Gardner et al., there is a problem of reproducibility in fabrication and, in addition thereto, electromigration problem is not considered.
The resistivity of wiring to electromigration may be improved by using, as the wiring, a three layer film composed of a titanium film sandwiched by aluminum-copper (Al-Cu) alloy films, as disclosed in U.S. Pat. No. 4,017,890 issued on Apr. 12, 1977 to J. K. Howard et al. and assigned to International Business Machines Corporation. However, the problem of increased resistance caused by making the titanium film thick can not be avoided by Howard et al.
Stress migration is considered as being produced by deformation of wiring due to thermal stress exerted thereon. Further, it has been considered that an aluminum-silicon-copper (Al-Si-Cu) alloy film is resistant to stress migration.
Although, as mentioned, effective approaches for solving the individual problems have been made respectively, any approach by which all of these problems are solved simultaneously has not been developed as yet.